Embodiments of the invention are directed to accelerated methods of determining the relative physical stability of a protein formulation and surfactant-stabilized insulin formulations.
The physical stability of pharmaceutical protein formulations is of paramount importance since there is always a time delay between production of the protein formulation and its delivery to an appropriate patient. The physical stability of a protein formulation becomes even more critical when using drug delivery devices to dispense the protein formulation, such as infusion pumps and the like. When these delivery devices are used, the protein formulation is generally stored in the device, which is either worn close to the body or implanted within the body. In either case, a patient""s own body heat and body motion, plus turbulence produced in the delivery tubing and pump, impart a high amount of thermo-mechanical energy to a protein formulation. Thus, the use of such infusion delivery devices places a high degree of thermo-mechanical stress on the protein formulation to be delivered. Additionally, infusion delivery devices expose the protein to hydrophobic interfaces that are found in the delivery syringes and catheters. These interfacial interactions tend to destabilize the protein formulation by inducing denaturation of the native structure of the protein at these hydrophobic interfaces.
Analytical tools for assessing the physical stability of protein formulations, in particular insulin formulations, have been developed. These analytical methods, however, generally require long test runs of 20 or more days, as well manual intervention during the test period. Moreover, most protein formulations contain numerous excipients that are added to the formulation to further stabilize the protein. For example, a typical insulin formulation may contain five or more excipients, such as a particular buffer system, isotonic substances, metal ions, preservatives and one or more surfactants.
Given the long test runs and manual intervention required to assess the physical stability of a new insulin formulation, as well as the need to vary five or more excipients over a particular concentration range during the analytical process, the development of new formulations is costly in terms of time and resources. Moreover, even for the evaluation of new batches of a known protein formulation, such as in quality control analysis, current state of the art methods are less than desirable.
Since the requirements of current protein formulation evaluation methods are not conducive to the rapid development of novel and more physically stable protein formulations, a reliable, time- and resource-efficient analytical method is desired. Such an analytical tool would enable the rapid development of novel protein formulations, as well as the rapid identification of protein formulation stability in quality control procedures.
Embodiments of the invention are directed to methods of evaluating the physical stability of a protein formulation. These methods includes two phases. The first phase includes the following steps. Preparing a statistically relevant number of identical samples of a protein formulation to yield a one or more sample types, where the protein is susceptible to changes in its native conformation yielding non-native conformers of the protein. A small molecular agent or probe that yields a change upon binding to a non-native conformer of the protein is then added to the samples. A controlled stress is then applied to all sample types, where the controlled stress applied causes the protein to exhibit a change in its native conformation. The sample types are then monitored to yield time-dependent data that are related to a degree of protein conformational change for each sample type. The second phase includes applying a survival analysis to the data obtained for each sample type and comparing the survival analysis for each sample type to determine the relative physical stability of the protein formulations under evaluation.
A preferred controlled stress suitable for use in embodiments of the invention is agitation. A preferred method to monitor the change in protein conformation is via fluorescence. An example of a protein conformational change suitable for use in the invention is the change in the physical structure of insulin from its native conformation to the fibril form of insulin.
From the use of a particular embodiment of the invention, novel surfactant-stabilized insulin formulations were developed. These novel insulin formulations include a buffer system, an isotonicity agent, a preservative, metal ions, and a non-ionic surfactant selected from at least a polysorbate, a poloxyethylene ether, a polyethylene glycol ether, and mixtures of these surfactants. The preferred insulin for use in these novel formulations is human insulin, preferably a human recombinant of insulin. The preferred insulin concentrations for use in the formulations of the invention is about 2 U/ml to about 1000 U/ml, most preferably about 400 U/ml.
An unexpected property of the novel surfactant stabilized insulin formulations of embodiments of the invention is that these formulations provide a greater stabilization to insulin than the prior art, Genapol stabilized formulations. Moreover, the surfactants suitable for use in formulations of the invention are FDA regulatory approved surfactants, thus further demonstrating the use of these novel formulations in pharmaceutical preparations of insulin.
These highly stable, surfactant-stabilized insulin formulations are particularly well-suited for use in infusion devices for the delivery of insulin to a patient. Thus, another aspect of the invention is directed to insulin infusion devices, which include an insulin pump system and a surfactant-stabilized insulin formulation including insulin and a non-ionic surfactant selected from at least a polysorbate, a poloxyethylene ether, a polyethylene glycol ether, and mixtures of these surfactants.